It is possible to compile the server with an option defining an
out-of-band prefix for commands. This is a string that the server will
check for at the beginning of every line of input from players, regardless of
whether or not those players are logged in and regardless of whether or not
reading tasks are waiting for input from those players. If a given line of
input begins with the defined out-of-band prefix (leading spaces, if any, are
not stripped before testing), then it is not treated as a normal command
or as input to any reading task. Instead, the line is parsed into a list of
words in the usual way and those words are given as the arguments in a call to
$do_out_of_band_command(). For example, if the out-of-band prefix were
defined to be `#$#', then the line of input

#$# client-type fancy

would result in the following call being made in a new server task:

$do_out_of_band_command("#$#", "client-type", "fancy")

During the call to $do_out_of_band_command(), the variable player
is set to the object number representing the player associated with the
connection from which the input line came. Of course, if that connection has
not yet logged in, the object number will be negative. Also, the variable
argstr will have as its value the unparsed input line as received on the
network connection.

Out-of-band commands are intended for use by fancy client programs that may
generate asynchronous events of which the server must be notified. Since
the client cannot, in general, know the state of the player's connection
(logged-in or not, reading task or not), out-of-band commands provide the only
reliable client-to-server communications channel.